Ever since its invention more than half a century ago, holography has been considered as a tool for three-dimensional (3D) imaging. In conventional holography, photographic films are used to record the holograms, which require chemical processing and significant investments of time. Reconstruction of the 3D images is also inconvenient, requiring proper illumination.
Recent trends in holography have focused on digital techniques for both recording and reconstruction. Off-axis digital holography is one such technique that has received much attention in recent years. In off-axis digital holography, the hologram is captured by a charge-coupled device (CCD) and reconstructed by virtual propagation in the software domain by a computer. Although off-axis digital holography can be used to create holograms of a target object, the method is suboptimal for two reasons. First, off-axis digital holography wastes the resolution of the CCD because of the necessity of recording carrier fringes produced by the angular separation between the object and reference beams. Second, the size of the object or reconstructed image is limited by the presence of the zero-order and conjugate images.
Because of those limitations, it is desirable to record in-line holograms using digital holography. This can be accomplished using phase-shift digital holography in which a piezoelectric transducer mirror is adjusted between exposures to shift the phase of the object wavefront. While phase-shift digital holography is well suited for static objects, its application to dynamic objects has been limited because it requires recording each phase-shifted hologram at a different time, and the object and reference beams do not share a common path. The non-common-path nature makes phase-shift digital holography susceptible to vibrations.
In view of the above discussion, it can be appreciated that it would be desirable to have a system or method for performing digital holography that avoids one or more of the drawbacks described above.